1. Field of the Invention
This invention relates to a method for producing a lithographic printing plate, more particularly to an improved plate-making method for obtaining a lithographic printing plate from a light-sensitive lithographic printing plate comprising a support, a non-silver light-sensitive layer and a gelatino-silver halide light-sensitive emulsion layer.
2. Description of the Prior Art
A light-sensitive lithographic printing plate comprising a support with a hydrophilic surface, such as an aluminum plate, a non-silver light-sensitive layer, such as a light-sensitive layer comprising an o-quinonediazide compound provided on the support and a gelatino-silver halide light-sensitive emulsion layer provided on the non-silver light-sensitive layer is known in the art as described, for example, in British Patent No. 1,227,603.
A method of producing a lithographic printing plate from such a light-sensitive lithographic printing plate fundamentally comprises the steps of:
(a) imagewise exposing the gelatino-silver halide light-sensitive emulsion layer,
(b) developing it to form a silver image,
(c) masking the silver image so obtained and exposing the non-silver light-sensitive layer to light,
(d) washing out the layer containing the silver image (i.e., the imagewise exposed and developed gelatino light-sensitive emulsion layer), and
(e) developing the non-silver light-sensitive layer.
In the prior art plate-making method, the washing-out at step (d) has usually been carried out by processing with hot water. The gelatino-silver halide emulsion layer cannot generally be dissolved and completely removed by such a treatment, i.e., usually it is removed in the form of small films which are remained undissolved. Thus, such a prior art plate-making method suffers from the disadvantage that where the washing-out is carried out mechanically in a processing apparatus, small pieces of the gelatino-silver halide emulsion layer as described above accumulate in the processing liquid, making it necessary to frequently change the processing liquid. Further, it has the disadvantage that the lithographic printing plate obtained by washing with processing liquid in which the identified small pieces have accumulated shows reduced lipophilic property in image areas, leading to a number of wasted sheets during the initial operation of printing.